Mass importation of thumbnails is a problem Scruffy Duck is working on for the next iteration of ADE. Meanwhile try bigthumb.zip in the Flightsim file library. I think it will contain all the autogen files you are missing and a lot more. Otherwise find a sparse airport in FSX ( I use L72 ) and start planting static objects one by one next to the runway and hand capture each thumbnail. (I started with hangars first and then a few objects like gas tanks and gas pumps) It is tedious but will work to get you started.
Hope this helps.
WinXP Pro SP3 Intel Core Duo CPU E7500
2.93ghz 4GB Ram ATI Radeon HD4350